1. Field of the Invention
The present invention relates to a rotary electro-dynamic machine and an armature winding thereof.
2. Description of the Related Art
A rotary electro-dynamic machine according to the prior art, as shown in a cross sectional view in FIG. 42, is constituted by a stator core 3 in which a winding slot 10 extending along the rotating shaft of a rotor, an armature winding 2 including an upper coil 2c and a lower coil 2d respectively constituted by many strand conductors 5 buried and piled in the winding slot 10, and plural ventilating ducts arranged in the radial direction in the stator core 3. The strand conductors 5 are formed so as to be twisted and transposed by 360 degrees continuously toward the extending or longitudinal direction of the winding slot 10 at a portion stored in the winding slot 10, and the strand conductors 5 are short-circuited at the ends of the armature winding 2 which protrude outward from the sides of the stator core 3.
When AC current flows through multiple strand conductors of such a configuration, a leakage magnetic flux that crosses the winding slot 10 in the circumferential direction occurs, thereby a voltage caused by EMF is induced to between the strand conductors 5 at each portion of the multiple strand conductors in the longitudinal direction. If, in a pair of strand conductors, there occurs an extremely large difference in the induced voltages of respective strand conductors in the entire length of the strand conductors, large circulating currents flow into the closed-loop shaped pair of strand conductors, so that current loss increases and heat which is generated inside of the strand conductors also increases.
Accordingly, in order to make almost same the voltage that is induced between the strand conductors over the entire length of the strand conductors and to prevent the circulating currents from flowing, the strand conductors are transposed by various methods.
Herein, with reference to FIGS. 43 and 44, transposition of strand conductors in the prior art will be explained. The transposition of strand conductors is made by twisting strand conductors along the extending direction of coil slot, and sequentially changing the rotational positions of the respective strand conductors. In the cross section of the strand conductors, a certain strand conductor is considered to move in a circular pattern around the center of the conductor cross section, and the transposition degree is expressed by the rotational angle thereof. The transposition where the respective strand conductors pass all the positions in the strand conductor cross section and get back to the same positions as those at which they have started at the opposite end of the winding slot is referred to as a 360-degree transposition.
FIG. 43 is a schematic diagram showing a strand configuration of a 360-degree transposition, and it is constituted by a stator core 3 in which plural winding slot extending along the rotating shaft center of an rotor (not shown), an armature winding 2 constituted by many strand conductors 5 buried and piled in the winding slot, and plural ventilating ducts 4 arranged in the radial direction in the stator core 3. The strand conductors 5 are formed so as to be twisted and transposed by 360 degrees continuously toward the extending direction of the winding slot at a portion stored in the winding slot, and the strand conductors 5 are short-circuited at the ends of the armature winding 2 which protrude outward from the sides of the stator core 3.
FIG. 43 shows a magnetic flux that cross between two representative strand conductors 5a and 5b. In the figure, crossing magnetic fluxes in the core section 3 are shown as 16a to 16c, and for example, the sum of fluxes 16a and 16c becomes equal to the flux 16b, and the induced voltage between the strand conductors 5a and 5b by the magnetic fluxes that cross in the winding slot is offset.
However, the 360-degree transposition has been applied in the winding slot, but has not been made outside the winding slot. Accordingly, there occurs unbalanced voltage due to leakage magnetic fluxes 16x and 16y at the end portions of the rotary electro-dynamic machine, and there occur circulating currents in the strand conductors 5a and 5b. 
As described above, since there are leakage magnetic fluxes at the slot end portion of such a rotary electro-dynamic machine, voltage is induced to the end portion of strand conductors, and circulating currents flow into the strand conductors and a current loss occurs. In order to reduce this loss, it is only necessary that the rotational positions or phases of the strand conductors at the end portions of the strand conductors are reversed, and that the directions of the respective voltages induced at the end portions of the same strand conductor are reversed so as to offset them. This is realized by a 540-degree transposition, i.e., one-and-half-turn transposition of the strand conductors in the winding slot.
FIG. 44 is a schematic diagram showing a strand configuration for a 540-degree transposition, and the same functional components as those shown in FIG. 43 are denoted by the same reference numerals, and the duplicated description thereof is omitted.
In FIG. 45, the transposition pitch in the area of ¼ of the core length from the end portions becomes a half of that at the center portion, namely, in the area of ¼ of the core length from the end portions and in the area of ½ of the core length at the center portion, a 180-degree transposition has been applied respectively. The sum of the crossing magnetic fluxes 16a and 16e between the strand conductors 5a and 5b becomes equal to 16c, and the sum of 16b and 16f becomes equal to 16d, so that the induced voltage between the strands 5a and 5b is offset in the winding slot. The crossing magnetic fluxes 16x and 16y are also offset each other outside the winding slot, it is possible to reduce the circulating currents due to leakage magnetic fluxes at the end portions of the strand conductors.
Besides, it is possible to reduce unbalanced voltage due to leakage magnetic fluxes at the end portions by a 450-degree transposition, and in principle a transfer of 360+90n degrees may be considered, while n is an integer other than 0.
Further, there is disclosed another prior art in which transition intervals of conductive strands are made uneven in a slot, and a portion transposed positionally in the circumferential direction and the radial direction and a portion not transposed are arranged to generate an unbalanced voltage in the conductive strands in the slot, so that unbalanced voltage that occurs in the conductive strands outside of the slot is compensated by the unbalanced voltage (refer to a prior art document 1: Jpn. Pat. Appln. KOKOKU Publication No. 58-14141).
In the invention of this document 1, since a portion not transposed is arranged in slot, the transposition pitch becomes short, and thus, there has been possibility that insulation of strand conductors may be broken, and the strand conductors may be short-circuited.
Moreover, there is disclosed still another prior art document 2 in which, in order to improve the problem with the first example, strand conductors are formed so as to be twisted and transposed continuously toward the extending direction of slot except both the end portions, the thicknesses thereof in the piling direction are made different, and strand conductors are arranged such that thick strand conductors arranged in the radial direction from the rotational center of the rotor at the end portions occupy the area closer to the rotor (refer to the prior art document 2: Jpn. Pat. Appln. KOKAI Publication No. 2002-78265).
On the other hand, there is a case where, in order to offset the leakage magnetic fluxes at the end portion side as shown in FIG. 43, the transposition angle is made slightly below or above the above-mentioned 360+90n degrees. In this case, normally, the transposition angle is determined such that the sum of the circulating current loss due to the induced voltage by the leakage magnetic fluxes at the end portion side, and the circulating current loss due to the induced voltage by the crossing magnetic fluxes in the winding slot becomes to a small value.
Next, cooling gas ventilation routes in a machine will be explained with reference to FIG. 45. FIG. 45 is a basic configuration example of cooling gas ventilation routes in a rotary electro-dynamic machine such as a turbine power generator.
The stator core of the rotary electro-dynamic machine, in which punched iron core plates are laminated, and inside interval pieces are inserted at a specified interval, forms a radial ventilation duct. The ventilation duct is divided into one or more sections in the axial direction, and separated into an air supply section that flows air from the outer peripheral side of the core to the inner side and an air exhaust section that flows from the inner side to the outer peripheral side. FIG. 45 shows a configuration example in which the stator core 3 is divided into two air supply sections 4a and three air exhaust sections 4b. 
Cooling gas or air is supplied by a rotor fan 11 attached at ends of the rotor, and branched into three directions to a rotor 1, an air gap 9 and an armature winding end portion 2b. 
The supply of the cooling gas to the stator is made from the ventilation route that flows from the fan 11 directly to the air gap 9, and by guiding cooling gas that has cooled the armature winding end portion 2b to the air supply sections 4a of the stator core 3.
The cooling gas supplied to the air supply sections 4a flows through ventilation ducts from the outer side to the inner side, and cools down the stator core 3 and the armature winding 2, and is then conducted to the air gap 9. In the air gap 9, the cooling gas that flows from the fans 11 directly into the air gap joints together with the exhaust gas from the rotor 1, and further flows through the air exhaust sections 4b from the inner side to the outer side, cools down the stator core 3 and the armature winding 2, and interflows at the outer side of the stator. The cooling gas that has cooled the stator and the rotator and become hot goes through a water cooling gas cooler 12 to be cooled down, and goes through air channels back to the rotor fans 11.
The temperature upper limits of the armature winding and the magnetic field winding are strictly limited according to the heat resistance performances of insulating materials that configure the armature winding and the field winding. In the design of the rotary electro-dynamic machine, it is necessary to design such that these temperatures are kept at the rated values or less.
In order to efficiently cool the armature winding, it is preferable to supply less cooling gas to portions whose winding temperatures are low and to intensively supply cooling gas to portions whose winding temperatures are high, thereby to equalize the winding temperatures.
As one of means for adjusting the supply amount of cooling gas, there is a method in which stator core ducts are arranged at uneven pitches in the axial direction. By way of example, a configuration example of a stator core in which ventilating ducts are arranged at uneven pitches is shown in FIG. 46.
Since the cooling gas that flows from the stator end portion into the air gap is supplied directly from the fans, the temperature thereof is lower than temperatures at other portions and is advantageous for cooling. Accordingly, the ventilating ducts 4 at the core end portion have been arranged at a larger pitch than that at other portions.
Further, the temperature of the cooling gas in the air supply sections is lower than that in the air exhaust sections, and thus, the duct pitch of the air supply sections is arranged larger than that of the air exhaust sections in some cases.
When, in the above-mentioned electro-dynamic machine and the armature winding thereof, the ventilating ducts of the stator are distributed unevenly in the axial direction, the distribution of the leakage magnetic fluxes that occur in the core section becomes uneven in the axial direction, and the balance between the magnetic fluxes that cross among strand conductors is lost. Therefore, there occurs unbalanced voltage among conductive strands, and circulating currents occur, and as a consequence, a loss distribution is caused in the conductive strands, and the conductors are subject to local overheat, which has been a problem in the prior art.